1. Field of the Invention
The present disclosure relates to new methods of directed self-assembly pattern formation in the fabrication of microelectronic structures and hardmask neutral layers for use in the same.
2. Description of Related Art
Currently, the genuine resolution limit for single patterning optical lithography techniques, using 193-nm immersion scanners is 37 nm for dense lines and spaces. However, a relatively new non-lithography patterning technique, called directed self-assembly (DSA), is already capable of forming patterns that are <15 nm. DSA harnesses the ability of some molecules to rearrange themselves into ordered, nanometer-scale structures. Such self-assembling molecules tend to form highly regular and extended arrays of alternating lines or tiled configurations of close-packed circles. Block copolymers containing at least two different components are suggested DSA materials which can be aligned using annealing. In general, self-assembly is based upon the affinity or preference of one of the blocks for the underlying surface and/or air interface. This typically results in parallel lamellar layers. Pre-patterning techniques, such as chemoepitaxy or graphoepitaxy, can be used along with DSA, to de-randomize the alternating patterns formed by annealing blocked copolymer layers, making this technology even more useful in IC manufacturing. In graphoepitaxy, topography on the wafer surface, such as photoresist lines/trenches, is used to guide the self-assembly process. Thus, DSA may be particularly useful for line/space frequency multiplication techniques. In chemoepitaxy, local variations in the surface energy of the layer to which the DSA material is applied dictate how the block copolymers will align. Due to the flexibility of this approach, DSA is quickly becoming a front running technology for forming patterns of <20 nm for integrated circuit (IC) manufacture, and these types of non-lithography techniques will become more and more important in the future.
However, current DSA process flows require the use of several layers, which can complicate the process. In particular, DSA of block copolymers typically requires an organic, neutral “brush” layer applied in the stack underneath the block copolymer layer to induce pattern formation in a manner perpendicular to the substrate surface. For a typical PS-b-PMMA block copolymer, this brush layer usually consists of a random copolymer of styrene and methyl methacrylate (PS-r-PMMA) that has been cured over a long period of time. The brush layer is typically applied over a stack already containing spin-on carbon, a hardmask layer, and a bottom anti-reflective coating (for lithography-assisted DSA techniques). The block copolymer DSA formulations are then coated to a thickness of around 200-400 Å on top of the brush layer and annealed. The annealing process causes the block co-polymer to arrange itself into alternating organized structures.
A conventional DSA process is depicted in FIG. 1. As noted above, a bottom anti-reflective coating is often used in the stack to control reflection during lithography pre-patterning. This pre-pattern is often formed by standard photolithography techniques, such as the patterning of a photoresist. Inorganic layers are also included in the process flow to facilitate the pattern transfer process (e.g., a CVD hard mask). Each of these layers increases the level of complexity in the process and the challenges for chemical matching between layers. The multiple layer process also increases the length of time and cost of the DSA flow.
Thus, there remains a need in the art for improved compositions and methods for DSA patterning of microelectronic substrates.